1. Field of the Invention
The present invention relates to the field of packaging, and more particularly to a machine for blow-molding articles such as containers.
2. Brief Discussion of the Related Art
Documents FR-A-2 851 227 and WO-A-2010/007004 disclose a method and a machine for blow-molding containers that are made from a strip of thermoformable material. The method is based on shaping the strip into a tube that is heated and then inserted into a mold. Air injected into the tube enables it to be deformed so as to press its wall against the inside surface of the mold cavity. That method is easier to implement than an extrusion blow-molding method and it enables a wider variety of shapes to be obtained than a conventional thermoforming method. In addition, the use of material in strip form and the limited stretching of the material make it possible to use a multilayer material.
The machine described in those documents comprises a mount having mounted thereon in succession along a rectilinear path for the strip through the machine: a blowpipe connected to an air manifold member and extending coaxially about a longitudinal direction of the strip; a shaper arranged around the blowpipe to bring the longitudinal edges of the strip close to each other in order to shape the strip into a tube around the blowpipe; a welder member for welding together the adjacent edges of the strip shaped as a tube; at least one heater member for heating the strip; a mold having two portions that are movable relative to each other; and a drive device for driving the strip along its longitudinal direction. The blower member, the welder member, the heater member, the mold, and the drive device are connected to a control unit that is arranged to control them in such a manner as to perform the blow-molding method.
It has been found that the performance of the machine depends very strongly on the regularity with which the material advances through the machine, with this applying both in terms of productivity and in terms of the quality of the containers that are obtained, in particular when the strip of material is printed.
Unfortunately, in that machine, the material is present in the form of segments that alternate between being flexible and rigid, namely:
a relatively flexible segment when the material is in the form of a strip;
a relatively rigid segment when the material is in the form of a tube upstream from the heater member;
a relatively flexible segment when the strip is in the form of a tube downstream from the heater member; and
once more a relatively rigid segment after blow-molding.
This alternation makes driving the material more complicated, in particular when a relatively high speed of advance is desired for the material through the machine, or when the strip is printed. It is necessary to avoid giving rise to excessive stretching of the flexible segments and to avoid forming creases therein.